1. Field of the Invention
Implementations of various technologies described herein generally relate to mud pumps, particularly duplex mud pumps.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
In extracting hydrocarbons, such as oil and gas, from the earth, it is common to drill a wellhole into the formation containing the hydrocarbons. Typically, a drill bit is attached to a drill string, including joined sections of drill pipe, which may be suspended from a drilling rig. As the drill bit rotates, the hole deepens and the string is lengthened by attaching additional sections of drill pipe. During such drilling operations, drilling fluid, or “mud”, may be pumped down through the drill pipe and into the hole through the drill bit. The circulating drilling fluid serves a multitude of purposes, including cooling and lubricating the drill bit, removing drill cuttings and transporting them to the surface, preventing ingress into the wellhole of unwanted material such as oil, water, and gas, and equalizing downhole pressure by providing downhole weight.
Reciprocating mud pumps are commonly used for pumping the drilling fluid. FIG. 1 illustrates a front view of a typical duplex mud pump 100. The pump 100 consists of a fluid end 160 and a power end 170. The fluid end 160 imports, pressurizes and exports fluid. The power end 170 includes a power source, typically a diesel engine, and a crank shaft 110 which transmits power and motion to a connecting rod 120. The connecting rod 120 articulates the motion of the crank shaft 110 to a crosshead 130. The crosshead 130 creates a linear reciprocating motion derived from the crank shaft 110 rotary motion through the connecting rod 120. The reciprocating motion of the crosshead 130 is applied to a piston 150 by a shaft 140. In the fluid end 160, the reciprocating piston 150 discharges pressurized fluid from a cylindrical liner block in the fluid end 160.
Mud pumps can be single acting, in which fluid is discharged on forward piston strokes, or double acting, in which each piston stroke, forward and backward, discharges fluid. A duplex mud pump has two double-acting reciprocating pistons disposed in two corresponding cylinders, each forcing fluid in one or more discharge lines.
Mud pumps typically operate at very high pressures in order to pump the drilling fluid through several thousand feet of drill pipe and still deliver the fluid at a relatively high velocity. In addition, the fluid that may be pumped may be corrosive and/or abrasive. The high pumping pressures and corrosive and abrasive nature of the fluid often cause washouts in the fluid end. Washouts are holes in pressure-containing components caused by erosion. Washouts in the pistons, cylinders, valves and other components of the fluid end may be the most common cause of mud pump fluid end failure. Duplex mud pump fluid ends are typically made from one piece of welded metal. When a washout occurs in a fluid end, the fluid end must be welded and repaired either by using a welder and portable boring system in the field or by moving the fluid end to a machine shop. Both of these methods are expensive and time consuming. It is, therefore, desirable to have a high-pressure, reciprocating, mud pump that can be easily and quickly repaired in the field and inexpensive to manufacture.